This application relates to appendages for sailing vessels with heavy ballast bulbs as required for large sailing yachts such as International America""s Cup Class (IACC) Yachts and in particular to rotatable fin keels for increasing their forward velocity by generating enhanced hydrodynamic forces and reducing drag so as to quicken the sailing vessel""s passage to a windward destination.
In this specification, the following terms have the following meanings: a xe2x80x9ccanoe bodyxe2x80x9d is the hull of the vessel up to the sheer line excluding appendages; an xe2x80x9cappendagexe2x80x9d means an underwater protrusion from the underside of the canoe body such as a keel, fin, wing, dagger board, centerboard keel, rudder, etc. (the ballast bulb is not an appendage); xe2x80x9cVMGxe2x80x9d (Velocity Made Good) means the velocity of a tacking or reaching sailing vessel towards its windward destination; xe2x80x9cleeward driftxe2x80x9d means the drift to leeward of a tacking or reaching vessel caused by the wind; xe2x80x9cappendage liftxe2x80x9d means a force generated by a submerged moving appendage in the direction to counter the leeward drift by the wind of a tacking or reaching sailing vessel; xe2x80x9cwetted surfacexe2x80x9d is any surface over which water passes; xe2x80x9cdragxe2x80x9d means the resistance of water passing over any submerged surface; xe2x80x9cappendage or keel dragxe2x80x9d means the resistance of water passing over wetted surfaces of a keel or an appendage; xe2x80x9cwater trackxe2x80x9d is the direction of the body of water moving towards and impinging upon a canoe body; xe2x80x9ccrabwise motionxe2x80x9d of a canoe body means that it is moving into the water track with its longitudinal axis at an angle thereto; xe2x80x9ccrabwise hull dragxe2x80x9d means the additional drag of the canoe body when it has crabwise motion; xe2x80x9cmaking leewayxe2x80x9d means that the keel or appendage is producing an asymmetrical effect to generate a hydrodynamic force vector having a component to counter the leeward drift; xe2x80x9cangle of incidence or xe2x80x9cleeway anglexe2x80x9d means the angle between the longitudinal centerline of a fin or appendage and the water track; an xe2x80x9casymmetric effectxe2x80x9d means the creation of a hydrodynamic force when the water track is split into two paths and then are reunited, one path of the water flow being longer than the other path of the water flow; a xe2x80x9csymmetrical appendagexe2x80x9d means an appendage having two opposite chord surfaces each with the same camber; xe2x80x9cfavorable wind shiftxe2x80x9d occurs when the apparent wind angle increases; xe2x80x9cLift/Drag Ratioxe2x80x9d means the quantity of lift per unit of drag produced by a moving submerged fin, the goal being to generate maximum lift with minimum drag by increasing the lift and/or reducing the fin drag; and the Velocity Made Good (VMG) of a tacking or reaching vessel is the component of the sailing yacht""s forward velocity vector which is directed towards the windward mark.
Skippers of racing yachts desire to win races and Skippers of cruising sailboats desire to shorten the time on tacking and reaching passages. Such goals can be favorably influenced with appendage design in accordance with the invention.
Naval Architects have been frustrated knowing that as little as increasing the forward yacht velocity by one half a knot will win races. One of the major problems is reducing the drag of the wetted surfaces of the ballast bulb support members.
It is a principal object of the invention not only to reduce the drag of the wetted ballast bulb support surfaces but to eliminate them.
Another object of the invention is to maintain desired leeway when the canoe body is turned directly into the water track.
Another object of the invention is to increase the Velocity Made Good (VMG) by eliminating the drag of the bow wave and reducing hull drag by eliminating crabwise motion of the yacht""s hull when it is tacking.
Still another object of the invention is to increase the velocity by turning the canoe body away from the wind and directly into the water track to produce a favorable wind shift without reducing its desired leeway or lengthening the path to the windward mark by maintaining a desired angle of incidence of the fin keel to the water track.
The rotatable fin and the fixed ballast bulb support are juxtapositioned to eliminate drag of the submerged fixed ballast support. While sailing, the submerged ballast support member has no wetted surface which would generate drag. A new and novel support structure fixed to the interior of the canoe body includes an elongated support member fixed to the canoe body which carries a heavy ballast bulb at its bottom end. A desirable thin hollow fin completely jackets the ballast support member and is rotatable thereabout to selective angular displacements from the longitudinal axis of the canoe body. The ballast support member is anchored to many regions in the interior of the canoe body to distribute large stresses and thus avoid destructive consequences. The rotatable fin extends upwardly into the interior of the canoe body to avoid water passage between the top of the fin and the underside of the canoe body. The ballast member is geometrically shaped as a four sided diamond to permit the required angular displacement of the fin while providing required high strength and great stiffness for the jacketed unit of the fin and ballast support member unit.
In addition to the fin reducing its leeward drift, its fin shape can increase the forward velocity of a tacking yacht as explained by the Law of Energy Transfers. Energy balance formulas are set forth to explain how the forward velocity of a tacking yacht is increased when its leeward drift is decreased by selectively shaping the fin for generating a desired asymmetrical effect about the fin.